At the present time, approximately 250 million scrap, used tires are generated each year in the United States and correspondingly high number of scrap tires are also generated annually elsewhere throughout the world. In the United States, about 15 percent of these tires are reused--most by burning to recover the energy content, with other uses including fabrication into other materials, reclamation for use as tires, and for use in asphalt rubber. The remainder of the used tires are either landfilled or stockpiled. Currently, approximately 2-3 billion tires are stockpiled in the United States, posing both an environmental and a health hazard.
Recycling of rubber tires with asphalt for road resurfacing and other uses has been attempted as a way to utilize the volume of scrap tires. However, problems exist with the cost and implementation of such compositions. The use of recycled rubber with cement and such additives as a bituminous binder and adhesives has been suggested to an extent in German patent specification 121744. The particulate rubber is stated as having a maximum grain size of about 25 mm, and no preferred particle size ranges are set forth.
A need exists in the field to provide a cementous composition containing a recycled particulate rubber which composition can be used for various road surface or structural applications. A particular area to be addressed is the determination of a type of particulate rubber that provides superior properties when admixed in a cementous composition.